Quality Control Has Machine Parts Producer Breathing Easy

Feb. 17, 2011
Using Stotz air gauges to validate spindle interface components, Advanced Machine & Engineering keeps quality at highest levels
HSK 125 spindle shaft ID taper check.

Stotz USA LLC supplies air gauging products and technology, and gauging system integration services. Chris Koehn, president of the Freeport, Ill., company, attributes its success to several factors, not the least of which has been the loyalty of customers who appreciate the value Stotz products brings to their own operations.

“We are constantly striving to improve our designs and develop new products to solidify our position as a leader in measuring technology,” according to Stotz president Chris Koehn. His company’s customers include top manufacturers and suppliers in the machine tool, automotive, aerospace and medical industries.

Among those customers is Advanced Machine & Engineering in Rockford, Ill., a company that Koehn knows and appreciates well, because he worked there, long ago.

AME is a global supplier of precision machine tool components and metal cutting solutions — including high-quality machine tool spindle interface components. It is recognized throughout the machine tool industry for manufacturing excellent power drawbars, spindle shafts, guide bushings, locknuts, hydraulic sleeves, expansion gibs, and more. Its components enhance the AME brand and affiliated brands, like OTT Jakob, Spieth and Tschudin & Heid, as well as Hennig, itself a major supplier of chip conveyor and machine protection systems.

AME had been a Stotz customer before Chris Koehn came to work at the air-gauging company, and now the two firms maintain a solid working relationship, for all the right reasons. AME demands the highest level of quality in its machining and finishing departments and Stotz air gauging systems make it possible to accomplish that every day, according to AME service manager, Greg Hobbs.

“Air gauging is the only technology we’ve found that’s accurate enough to check the machine tooling and especially the spindle tapers we produce here. That’s a fact. In the past, we’d use hard gauges and we still use them, but only for certain OD checks. We’d blue-up the tapers, insert them, give them a good twist and do our inspections. … Way too much inconsistency.

“Today,’ Hobbs continued, “with sophisticated HSK tooling, this method is too hit-or-miss to be reliable. Air gauging provides dead stops on the test stand and the documentation is unbeatable for validation on the straightness, surface finish and taper angles. Plus, the Stotz system allows us to upload all the data on every part, so we have our favorite word — documentation — for every part we produce.”

A Stotz MRG air column displays all values for surface finish, taper angle, and straightness.

Hobbs also commented on the user-friendliness of the Stotz air column. When the program is first input into the column for a part in the AME grinding department, for example, the Stotz column essentially becomes a PLC, providing hard data via the Ethernet connections to the host data base. In this manner, every parameter of every part is documented and recorded. In a classic example of the law of unintended consequences, this process is not only used on the parts run, it’s also used for calibrating the AME machines, in a predictive maintenance function.

At AME, various testing of machined spindle interface and other components is performed both at the machines in the grinding department, in a temperature-controlled 72°F environment, plus in the company’s totally environment-controlled in-house testing department, supervised by the company’s director of quality, Brad Patterson. He confirmed Greg Hobbs’ observation that numerous other technologies have been investigated over the years for quality checking at AME and that air gauging has been found to be the best and most reliable for this company’s applications, particularly ID dimensions and configuration.

Patterson also credited the sophistication of the Stotz air column. “We get all the data required and we get it in exactly the fashion needed to support our customers,” he said. “Repeatable results and elimination of error, every time. Plus, the set-up is much faster than on our laser mics, which can’t be used for ID measurement.” He also noted that replacing the bluing technique, one he termed a “black art,” with air gauging has brought AME up to the most current industry standards for quality evaluation, and maintains that standard.

The typical Stotz air column found here is the Model MSG, with four pneumatic channels or 10 LVDT channels operating simultaneously, pneumatic length measuring, user specific programming up to 18 programs per column, full statistical analysis, and full data transfer capability within the host network. All info is fed into the AME host computer by serial number, so any job can be quickly retrieved, while historical records on any part produced can be easily called up for evaluation, deviation claims or to dovetail with a customer’s internal quality protocols.

Typically, as AME’s grinding supervisor Sam Schubert explains, the finished product will rest for 24 hours of soaking, allowing the diameters to normalize. Though statistically predictable for most metal materials, thermal expansion can cause off-normal readings to occur. For checking certain bearing journals or spindle shafts, snap gauges are set to accommodate size measurements down to the 20-millionths (0.000020-in.) range. The acceptable diameter tolerances for most AME products measured are in the 1-2 tenths (0.0001-0.0002-in.) range.

In cases where new masters are made for setting control values, those values are preset offline and programmed into the air column’s software, according to Greg Hobbs. Stotz typically performs this function for the customer in a remote manner over the Internet, through a proprietary IP address.

In the foreground, the HSK 40 grind quill. In the background, ANSI B 5.50 40 taper balance plug.

Among the many products finished in this grinding department are CAT/ISO 40 taper spindles, HSK test arbors, HSK grind quills, HSK steep taper milling tools and more. Often, older and worn spindle shafts are reverse engineered by AME for retrofits and reman’s. Even in these cases, air gauging is used to evaluate the finish process on the ID taper, as this versatile technology is easily adapted to such applications, according to AME personnel.

Sam Schubert expanded on the use of Stotz air gauging at AME.

“We have a full and very expensive inventory of hard gauges with state-of-the-art indicators attached.” Schubert said, “but the air gauges can do so much more. We use them for set-up on the grinding machines and they save us hours, every week. When you run the number of jobs we do here, that translates into substantial, additional work product and therefore more revenue for the company. In terms of reliability, some of the Stotz air gauges we run here have been at AME since we began using the technology, nearly ten years ago now.”

Schubert also noted the air gauging set-ups on the grinders dramatically reduce the time to first part in his department’s operation.

On one important spindle-shaft project for an Asian machine tool builder, which was looking for a U.S. source of supply, Schubert notes, AME was confronted with an unusually large quantity run, where tool degradation during the run would normally impact the production at some point. After an initial batch was produced, the machine builder claimed that everything but the taper was satisfactory. Quite surprised by this claim, AME checked all the documentation and determined that the customer’s test unit was actually out of spec, in a case where the error was repeated consistently, and thus overlooked. In the end, the AME products were deemed better than perfect, in that instance.

Sam Schubert cited a useful analogy: “The documentation we can produce from the air gauging procedure is like a birth certificate on every unit we make. All our spindle shafts for customers, for example, can be viewed as a series of genetically identical twins to each other and we’re providing the documentation of their DNA.”

As evidence of their commitment to this technology, Schubert noted that AME is now purchasing air gauging fixtures for all new customer applications. This quality spindle interface manufacturer aims to “keep breathing easy” in their process and product validation, as a result.

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